Protostar Monosynth

Protostar patchable monosynth

New year, new progress, and a little blog redesign! :)

The instrument shown on the pictures is the Protostar patchable monosynth. It's a usable, but work in progress synth, with the following features:
  • 2 VCOs
  • 2 suboctave generator with square waveform, -1/-2 octave
  • Waveform mixer with noise (4 waveforms/VCO + sub) with gain to overdrive the VCF
  • Minimoog VCF clone
  • 2 VCLFOs with 4 waveform outputs.
  • 2 ADSRs (one for the VCF, one for the VCA)
  • 3 VCAs

The signal path is normalized, based on the traditional VCO-VCF-VCA signal routing of the classic monosynths. The LFOs is modulating the VCO's PWM, the ADSRs is dedicated to the VCF/VCA. All of the signals can be separated, all of the modules are possible to disconnect, thanks to the switching jacks.

Almost all of the modules are based on the great YuSynth designs, so thanks fly to Yves Usson!

Planned modules: Midi2CV (normalized to the VCO/ADSRs), mixers, multiples, external input preamp.

The front panels are laser engraved, made from anodized aluminum. The case is temporary.


Drum synthesizer - Finished

The case is ready, and all functions are working! :) There are small problems, but I will fix them soon.

It's really fun to play with it, especially the cross-modulation functions, and the triggering combined. It can produce sounds from funny, and simple synthetic "space" drum sounds, to agressive, and noisy, industrial drums, even cool analog bass sounds, and simple synth sequences! So much possibilities are in this "simple" instrument. :)

A little summary of the instrument:

Rebel D2 logo

Analog drum machine, and filterbox.

  • Two independent drum channels, based on Coron DS8 design.
  • Two Wasp VCF clones, with LP/HP/BP/Notch modes
  • External signal processing with the filters
  • Triggering with button, or external signal (audio, piezo pulse, etc.), led indicator
  • Inputs for VCO frequency CV
  • VCO frequency modulation (or cross-modulation), with VCF output of the other channel
  • VCF CV input
  • Separate outputs, or mixed out

Sound samples will follow soon!


New modular case

This is the end of the lifecycle of my old, temporary case! Hooooraaay! :) Here is the new one!

I wanted to separate the PSU, and move out of the modular's box. My PSU is too strong, to power only one case, and the modules can occupy more space, if the PSU is not built into the case.

My new panel format is a nonstandard 160x160 mm, this case is built for them. The old modules will be cut to this size, or if it's not possible, they will be converted/reassembled soon.

Cheap materials.

The frame assembled.

Old, and new.

The PSU box, painted with a solar flare.

The new case, painted.

Populated with some modules.


My first multitracked "music" with the DIY modular

In this song i've used the following YuSynth modules: VCOs, EMS VCF, ADSRs, a mixer, and a VCA.


Magic Smoke 8K LFO

For the next module, which I want to build, i've needed a simpe LFO with speed control only. After hours of browsing the schematics, i've found Tim Servo's MSE 8K LFO. This circuit can do triangle and square waveforms, and it's high range, but with only one pot it's hard to fine tune on the lower end. The schematics shows a fine tune pot, but i don't want to include it, because of the limited front panel space.
It's very easy to build, only a TL072 or 074 opamp is needed. I've integrated a simple led driver too.
With polyester caps, the triangle waveforms are perfect, of course ceramics don't do it very well.
My version uses 1nF timing caps, and this gives 15 sec with the lowest pot setting, which is perfect for me.

More schematics, simple LFO's, and waveshapers for this LFO are here.

Thanks to Tim Servo, for his great work!

Dual LFO's on breadboard
Only a 1M Log pot, and an LED

Some power distributors added


My new module: Mixer, MidiCV

This is a combined module, which contains a 6 input mixer, a monophonic Midi2CV converter (MCV-628), and an input preamp.

My new, non-standard panel format is 160x160 mm, fixed. I've bought a 20 aluminium panels, and I will repanel the old blue modules. I need to do this, because the old panels are weak, and inaccurate.


Drum synthesizer - construction 3

The front panel is ready, and the drum synth has a new PSU too. The electronics is completed, now I need to design a case.


Drum synthesizer - contruction 2

I've finished the rewiring of the panels, and the drum synth is now working with it's own external 9V DC PSU. Two separate piezo triggers can be used to fire the channels independently, it's a lot of fun. :) Sadly, the DS8's output signals are too quiet, or not ideal for the Wasp VCF, even if resistor R30 (100K) is replaced by a 470K one.

I also need to process external signals, so a preamp will be included:

Preamp, and mixer circuit on veroboard:


Drum synthesizer - construction 1

I'm in the middle of the building phase. The two drum voices (with the Wasp filters) are working properly! :)
I've made a temporary, cardboard faceplate, because I need to finalize the graphics. I need to make an extra PCB with the VCF LFOs (4069 LFO), some preamp for external input signals, a 555 negative supply circuit, and maybe a headphone preamp too. I also need to make some experiments with cross-VCO modulation between the two DS8s. If it sounds good, I will put 2 pots on the front panel with this functionality. I will make experiments with Wasp out -> DS8 VCA in feedback loop. I like distortion... :)


The "Rebel.D2" drum synthesizer

I like to run projects in parallel, so there is my new idea: I want a simple, analog drum synthesizer.

I've built a Coron DS8 clone from Marc Bareille's schematics. I don't have CA3080 OTAs, so I've redrawn the circuit to use LM13700, and integrated a led driver for the incoming trigger signals.
After a few hours of playing with the DS8, I've realized, that this circuit can be enhanced with a VCF. The DS8 doesn't contains a filter, only the noise spectrum can be altered with a switch.

Because the DS8 is using +5V supply voltage, and the Wasp VCF also using this value, I've tried it, and built this combination, plus a piezo trigger pad into a temporary plastic case for trial.
This combination sounds wonderful, warm, and analog, but it also can be harsh, distorted and rude. This VCF simply mutiplies the possibilities of the DS8.

Then the idea of a simple two channel drum synthesizer was born:

I don't want to integrate any control circuit into this machine, only the CV/control/trigger jack sockets will be built in. The Wasp filters can be used for external signal processing, so this unit will be an integrated drum synth and a dual filterbox.